# Calculate the resistance

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1. Jun 19, 2016

### diredragon

1. The problem statement, all variables and given/known data
In the picture below, is a circuit of constant direct current. The receiver is made of a changable resistor with resistance R. If the reciever delivers maximum electrical power its resistance is
a)9 b)6 c)3 d)1.5 e)0.5
2. Relevant equations
Im having trouble finding the equation for this
3. The attempt at a solution
I cant find the theory of this curcuit, the equations that fit so can you guide me a little in any way that could help?

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2. Jun 19, 2016

### cnh1995

Look up 'maximum power transfer theorem'. Are you familiar with the Thevenin's theorem?

3. Jun 19, 2016

### diredragon

I am not but i will check it out now then try to apply something to the problem and get back to you :)

4. Jun 19, 2016

### diredragon

5. Jun 19, 2016

### cnh1995

For maximum power transfer, the load resistance should be equal to the Thevenin resistance of the circuit viewed from the load terminals. Here, your load resistance is the variable resistor. Can you proceed with this?

6. Jun 19, 2016

### diredragon

Is the equation for thevenin resistance the one in the picture uploaded? If so how to get it if not all three resistors are known?

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7. Jun 19, 2016

### cnh1995

For computing Thevenin resistance seen from the load terminals, you should remove the load resistance (variable resistance) and compute the resistance of the circuit seen from the load terminals.